In this proposed research we are applying genetic and biochemical approaches to the study of amino acid transport in Escherichia coli. We are characterizing the number of transport systems for leucine. It was determined that leucine is transported by two types of systems, one of which is membrane-bound and the other type of system requires the leucine-binding proteins. The present study will attempt to determine the similarities and differences in these two types of transport systems. Using genetics we hope to determine the number of components of each system and, through biochemical studies, to isolate some of the components of the transport system. We will isolate the three binding proteins that serve as the receptor site for three of the transport systems and study the chemical and physical properties. Experiments of this type on microorganisms should provide information that can serve as a basis for the study of transport in animal tissues. Since certain human diseases are caused by defects in transport, this work is expected to provide approaches for examining transport in more complex tissues.